Artist's rendering of quantum entanglement.
A team of researchers at the University of Tennessee at Chattanooga, along with those at the Oak Ridge National Laboratory (ORNL) and utility company EPB, have successfully developed and tested the first-ever transmission of a quantum entangled signal over a commercial network.
This is an important step in creating a quantum internet network that is more secure and capable than existing networks.
Quantum computing uses quantum bits or qubits to store information. Unlike classical binary bits, qubits can exist in more than one state at one time, allowing combinations of physical values to be encoded to a single object. Qubits can also be entangled, transmitting information from one place to another without physically traveling the distance.
Known as quantum teleportation, this is an important component of a quantum-based network. Light particles or photons can be used as qubits in their polarized forms and transmitted using existing fiber-optic cables, much like classical computing data.
However, changes in conditions such as wind, moisture, or even temperature can change the polarization of light and interfere with the signals transmitted. Collaborative research by scientists based at Chattanooga and ORNL worked to address these issues in the existing networks.
Avoiding periodic shutdowns
Joseph Chapman, a quantum research scientist at ORNL, explained that most previous solutions didn’t work for all polarization types.
He said in the press, “Most previous solutions didn’t necessarily work for all types of polarizations and required trade-offs like periodically resetting the network. People using the network need it up and running.”
With Muneer Alshokwan, another research scientist at ORNL, Chapman used automatic polarization compensation (APC) to stabilize the polarization of light waves sent over EPB’s commercial-grade fiber-optic network.
APCs can reduce data inference caused by external factors such as wind and temperature. The team used reference signals generated by lasers to check transmitted polarization continuously. This was verified using an approach called heterodyne detection.
“An experienced musician with a good ear can tell the difference when two instruments are out of tune,” Chapman added. “In our APC, we’re using a laser to do the same thing with our reference signals.”
Using entanglement-assisted quantum process tomography, the researchers estimated the properties of the quantum channel. They found that the transmissions remained relatively stable when APC was added, and the noise was minimal.
“Our approach controls for any type of polarization and doesn’t require the network to periodically shut down,” added Chapman.
The test utilized EPB’s fiber-optic commercial quantum network and involved the University of Tennessee Chattanooga and industry partner Qubitekk. Credit: Joe Chapman, Morgan Manning/ORNL, U.S. Dept. of Energy.
Working towards a quantum internet
Using their approach, the teams successfully transmitted quantum-entangled signals between nodes at the University of Tennessee Chattanooga campus and two other EPB quantum network nodes, each about half a mile away.
“This is the first demonstration of this method, which enabled relatively fast stabilization while preserving the quantum signals, all with 100% uptime – meaning the people at either end of this transmission won’t notice any interruption in the signal and don’t need to coordinate scheduled downtime,” added Chapman.
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The researchers have now applied for a patent for their approach. They will work on increasing the bandwidth and compensation to achieve higher-level performance, irrespective of the environmental conditions.
“Working with organizations like ORNL provides valuable feedback on how we can continue to enhance EPB Quantum Network as a resource for researchers, startups, and academic customers,” concluded David Wade, EPB’s CEO, in the press release.
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Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
